Glycosyltransferase gene

ABSTRACT

The present invention provides an enzyme which catalyzes a reaction to transfer sugar to a hydroxyl group at position 2′ of chalcones and a gene thereof, and preferably an enzyme which catalyzes a reaction to transfer glucose to a hydroxyl group at position 2′ of the chalcones. Furthermore, the invention provides a plant whose flower color has been changed using the glycosyltransferase. Using probes corresponding to conservative regions of the glycosyltransferase, some tens of glycosyltransferase genes having nucleotide sequences corresponding to the conservative regions were cloned from flower petal cDNA libraries of carnation and the like. Furthermore, each of the glycosyltransferase genes was expressed in  Escherichia coli , activity to transfer glucose to position 2′ of the chalcone, i.e., the glycosyltransferase activity at position 2′ of chalcone was confirmed in an extract solution of the  Escherichia coli , and it was confirmed that cloned genes encoded the glycosyltransferase at position 2′.

TECHNICAL FIELD

The present invention relates to a gene of an enzyme having an activity which transfers sugar to chalcones and a plant whose flower color has been converted by taking advantage of the glycosyltransferase. More particularly, the invention relates to a gene of an enzyme having an activity which synthesizes a glycoside at position 2′ of the chalcones, preferably a gene of an enzyme having the activity which synthesizes the glycoside at position 2′ of the chalcones derived from a carnation or a cyclamen, and the use thereof.

BACKGROUND ART

Flower color is an important character when people appreciate or buy flowers and ornamental plants, and the flowers with various colors have been bred traditionally. It is rather rare that a single kind of species has flowers with all colors, and this is due to the fact that biosynthesis of pigments (flower pigments) expressed as the flower colors is genetically defined. It has been substantially impossible to make the flowers with all colors in the target species by crossing because gene resources available for cross breeding are limited to related interfertile species. Only recently, it has become possible to modify the flower color by taking advantage of the gene recombination technology, obtaining a gene of an enzyme involved in synthesis of the flower pigment, and expressing the gene in other species (e.g., Non-patent Document 1, Non-patent Document 2).

Among the flower colors, an orange, red, purple and blue colors are primarily derived from flavonoid referred to as anthocyanin. A yellow color is often derived from compounds such as carotenoid and betalain other than flavonoid, but the yellow color of some plant species is derived from flavonoid. For example, it is known that a glycoside having sugar at position 2′ of 4,2′,4′,6′-tetrahydroxychalcone (THC) is present in petals of a yellow carnation (e.g., Non-patent Document 3). As chalcones, glycosides of THC, butein, and isoliquitigenin are known. As aglycones of the glycosides, The THC is contained in carnation, morning glory, peony, aster and strawflower, 3,4,2′, 4′, 6′-pentahydroxychalcone is contained in snapdragon and statice, the butein is contained in cosmos and Jerusalem artichoke, and the butein and isoliquitigenin are contained in dahlia. In limited species such as snapdragon, yellow flower pigment referred to as aurones such as aureusidin and brackteatine is present. An absorption maximum of the aurones is 399 nm to 403 nm whereas the absorption maximum of the chalcones is 365 to 382 nm, and thus color tones of both are different (e.g., see Non-patent Document 4). Generally in plant cells, the chalcones and the aurones are stabilized by becoming sugar-transferred glycosides, migrate to and are accumulated in vacuoles. Biosynthetic pathways of anthocyanin are well studied, and enzymes involved in the biosynthesis of anthocyanin and genes encoding them are known (e.g., see Non-patent Document 5). Enzymes involved in the biosynthesis of the aurone and genes thereof have been reported (e.g., see Non-patent Document 6).

The biosynthetic pathways of the flavonoids are present widely in higher plants and common between the species. The THC is biosynthesized from three molecules of malonyl-CoA and one molecule of coumaroyl-CoA by catalysis of chalcone synthase. As shown in FIG. 1, The THC exhibits pale yellow color, but in the plant, it is rapidly converted to colorless naringenin by chalcone isomerase. The THC is also extremely unstable at pH around a neutral, and is converted to naringenin by spontaneously closing a ring. In order for THC to be present stably in the plant cell, i.e., stably exhibit the yellow color, it is described that it is necessary that glycosyltransfer takes place at position 2′ of THC and the THC is transported into the vacuole. Therefore, it has been believed that if a gene of the enzyme which transfers the sugar to the position 2′ of the THC can be obtained, flowers with yellow color can be made by expressing this enzyme gene in the plant and accumulating THC glycoside (e.g., see Non-patent Document 7).

However, it has been impossible to measure an activity of the enzyme which catalyzes a reaction to transfer the sugar, e.g., glucose to a hydroxyl group at the position 2′ of the chalcones including the THC. Conventionally, the activity of chalcone glycosyltransferase has been measured by labeling UDP-glucose with a radioisotope, performing an enzymatic reaction, subsequently extracting a produced glycoside with ethyl acetate and measuring a radioactivity in an extracted organic layer (e.g., see Non-patent Document 8). However, most glycoside of the THC is moved to an aqueous layer, and thus it is most likely that glucose whose radioactivity has been counted is unreacted free UDP-glucose which has been slightly eluted in the organic layer. Therefore, there has been a problem that the original activity of THC glycosyltransferase can not be measured accurately. Accordingly, the enzyme which catalyzes this glycosyltransfer reaction could not be purified, and thus the gene encoding the glycosyltransferase could not be cloned.

It is known that the petals also become the yellow color when a compound where hydroxyl group at position 2′ of THC is methylated is accumulated, but neither enzyme which catalyzes this methylation nor gene thereof are known. 6′-Deoxychalcone is contained in yellow varieties of the dahlia and cosmos. In legume, 6′-deoxychalcone is a precursor of 5-deoxyflavonoid and is biosynthesized by catalysis of chalcone synthase (CHS) and chalcone reductase (CHR). It has been reported that a CHR gene of alfalfa was introduced into petunia and then 6′-deoxychalcones such as butein were synthesized. However, when the CHR gene was introduced into the petunia with white flowers, extremely pale yellow color was observed in flower buds, but bloomed flowers were almost white. Thus, this attempt did not lead to production of industrially useful yellow flowers (e.g., see Non-patent Document 9).

Enzymes which catalyze the glycosyltransfer reaction of various flower pigment compounds including flavonoid to produce the glycosides are referred to as glycosyltransferases. The plants have the glycosyltransferases of various molecular species having specificity depending on kinds of the aglycone and the transferred sugar, and genes encoding them. Glucose transferase usually utilizes UDP-glucose as a glucose donor, and thus the glucose transferase includes a motif to bind to the UDP-glucose in an amino acid sequence thereof (e.g., Non-patent Document 10). It is known that there are 99 kinds of genes for the glycosyltransferases having this motif in Arabidopsis whose genomic structure has been already shown entirely (e.g., see Non-patent Document 11). The amino acid sequences and functions in some glycosyltransferases have been elucidated. Genes of an enzyme (UDP-glucose: flavonoid 3-glycosyltransferase) which catalyzes a reaction to transfer the glucose to the hydroxyl group at position 3 of the flavonoid or anthocyanidin have been obtained from maize, gentian and grape (e.g., see Non-patent Document 11). Genes of an enzyme (UDP-glucose: anthocyanin 5-glycosyltransferase) which catalyzes a reaction to transfer the glucose to the hydroxyl group at position 5 of anthocyanin have been obtained from perilla and verbena (e.g., see Non-patent Document 12).

From analyses of the amino acid sequences of these glucose transferases, it has been know that proteins having the same function which catalyzes the glucose transfer reaction are similar in amino acid sequences even when the plant species are different, i.e., the proteins form a family (e.g., see Non-patent Document 11). That is, it has been reported to obtain the enzymes (ortholog) having the same function as that of the glucose transferase where the amino acid sequence and catalysis of the glucose transfer reaction were demonstrated, from the other plant species. For example, the gene of UDP-glucose: anthocyanin 5-glycosyltransferase in the petunia was cloned using the gene of UDP-glucose: anthocyanin 5-glycosyltransferase in the perilla (e.g., see Non-patent Document 13). However, even at a current technical level, numerous trials and errors as well as difficulties are involved in acquisition of the gene of glycosyltransferase whose amino acid sequence or function is unknown. In particular, the flower of Arabidopsis is white, and no accumulation of chalcone glycoside having the sugar at position 2′ has been reported. Therefore, the gene can not be cloned by taking advantage of information for the glycosyltransferase genes of Arabidopsis whose genomic structure has been already determined entirely. Concerning the carnation, it has been reported that when mutation occurs in a chalcone isomerase gene and dihydroflavonol reductase gene, the THC glycoside is accumulated to exhibit the yellow color. In the cyclamen, it is also believed that the THC glycoside is accumulated by mutation of chalcone isomerase. Likewise, as the plants in which the chalcone glycoside having the sugar at position 2′ is accumulated, petunia pollen, Paeonia lactiflora, strawflower, China aster, cyclamen, evening primrose and periwinkle are known. It is also believed that the gene of the enzyme which transfers the sugar to the position 2′ of THC is expressed in numerous plants, particularly the plants which exhibit the yellow flower color.

Non-patent Document 1: Plant Cell Physiol., 39:1119 (1998)

Non-patent Document 2: Curr. Opin. Biotechnol., 12:155 (2001)

Non-patent Document 3: Phytochemistry 5:111 (1996)

Non-patent Document 4: Biohorti I 49-57, Seibundo Shinkosha (1990)

Non-patent Document 5: Comprehensive Natural Products Chemistry, Vol. I (ed., Sankawa) pages 713-748, Elsevier Amsterdam (1999)

Non-patent Document 6: Science 290:1163 (2000)

Non-patent Document 7: Biotechnology of Ornamental Plants (ed., Geneve, Preece and Merkle) pages 259-294, CAB International Wallingford, UK (1997)

Non-patent Document 8: Phytochemistry 17:53-56 (1978)

Non-patent Document 9: Plant J., 13:259 (1998)

Non-patent Document 10: Plant Physiol., 112:446 (2001)

Non-patent Document 11: J. Biol. Chem., 276:4338 (2001)

Non-patent Document 12: J. Biol. Chem., 274:7405 (1999)

Non-patent Document 13: Plant Mol. Biol., 48:401-11 (2002)

DISCLOSURE OF THE INVENTION

The present invention provides an enzyme which catalyzes a reaction to transfer sugar to a hydroxyl group at a position 2′ of chalcones and a gene thereof, and preferably an enzyme which catalyzes a reaction to transfer glucose to a hydroxyl group at the position 2′ of the chalcones and a gene thereof. Furthermore, the invention provides a plant whose flower color has been modified, preferably changed to yellow color using the glycosyltransferase gene.

As described above, no character of glycosyltransferase on position 2′ of chalcone has been known, no enzyme has been purified and no gene thereof has been cloned. Using a probe corresponding to a conservative region of the glycosyltransferase from cDNA library of carnation petals, the present inventors cloned several tens of glycosyltransferase genes having nucleotide sequences corresponding to the conservative regions. Furthermore, the present inventors expressed the glycosyltransferase group in Escherichia coli, identified activity to transfer glucose to the position 2′ of chalcone, i.e., a glycosyltransferase activity on position 2′ of chalcone in an extracted solution of Escherichia coli, identified that cloned genes encoded the glycosyltransferase at position 2′, and completed the invention.

That is, the present invention is:

(1) A gene encoding a protein comprising an amino acid sequence described in SEQ ID NO:2 or an amino acid sequence having deletion, substitution and/or addition of one or more amino acid residues in the amino acid sequence and having an activity to transfer sugar to position 2′ of chalcones.

(2) A gene which hybridizes with DNA comprising a nucleotide sequence complementary to a nucleotide sequence described in SEQ ID NO:1 under a stringent condition and encodes a protein having an activity to transfer sugar to position 2′ of chalcones.

(3) A gene encoding a protein comprising an amino acid sequence described in SEQ ID NO:15 or an amino acid sequence having deletion, substitution and/or addition of one or more amino acid residues in the amino acid sequence and having an activity to transfer sugar to position 2′ of chalcones.

(4) A gene which hybridizes with DNA comprising a nucleotide sequence complementary to a nucleotide sequence described in SEQ ID NO:14 under a stringent condition and encodes a protein having an activity to transfer sugar to position 2′ of chalcones.

(5) A gene encoding a protein comprising an amino acid sequence described in SEQ ID NO:17 or an amino acid sequence having deletion, substitution and/or addition of one or more amino acid residues in the amino acid sequence and having an activity to transfer sugar to position 2′ of chalcones.

(6) A gene which hybridizes with DNA comprising a nucleotide sequence complementary to a nucleotide sequence described in SEQ ID NO:16 under a stringent condition and encodes a protein having an activity to transfer sugar to position 2′ of chalcones.

(7) A gene encoding a protein comprising an amino acid sequence described in SEQ ID NO:19 or an amino acid sequence having deletion, substitution and/or addition of one or more amino acid residues in the amino acid sequence and having an activity to transfer sugar to position 2′ of chalcones.

(8) A gene which hybridizes with DNA comprising a nucleotide sequence complementary to a nucleotide sequence described in SEQ ID NO:18 under a stringent condition and encodes a protein having an activity to transfer sugar to position 2′ of chalcones.

(9) A gene encoding a protein comprising an amino acid sequence described in SEQ ID NO:21 or an amino acid sequence having deletion, substitution and/or addition of one or more amino acid residues in the amino acid sequence and having an activity to transfer sugar to position 2′ of chalcones.

(10) A gene which hybridizes with DNA comprising a nucleotide sequence complementary to a nucleotide sequence described in SEQ ID NO:20 under a stringent condition and encodes a protein having an activity to transfer sugar to position 2′ of chalcones.

(11) A gene encoding a protein comprising an amino acid sequence described in SEQ ID NO:56 or an amino acid sequence having deletion, substitution and/or addition of one or more amino acid residues in the amino acid sequence and having an activity to transfer sugar to position 2′ of chalcones.

(12) A gene which hybridizes with DNA comprising a nucleotide sequence complementary to a nucleotide sequence described in SEQ ID NO:55 under a stringent condition and encodes a protein having an activity to transfer sugar to position 2′ of chalcones.

(13) A vector comprising the gene according to any one of (1) to (12) above.

(14) A host cell transformed with the vector according to (13) above.

(15) A method for producing a protein characterized by culturing or growing the host cells according to (14) above and collecting the protein having an activity to transfer sugar to position 2′ of chalcones from the host cells.

(16) A protein obtained by the method according to (15) above.

(17) A plant into which the gene according to any one of (1) to (12) above has been introduced, a plant which is a progeny of the plant, or tissue of the plant.

(18) A cut flower collected from the plant according to (17) above.

(19) A plant of which flower color has been modified by introducing and expressing the gene according to any one of (1) to (12) above into the plant, and a plant which is a progeny of the plant.

(20) The plant according to (18) above characterized in that a modified flower color is yellow.

According to the present invention, a novel gene and an enzyme are provided, the sugar may be specifically transferred to the hydroxyl group at position 2′ of chalcones, and the chalcones may be stabilized. The invention is used suitably for production of the plant whose flower color is modified.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing a synthetic pathway of chalcone glycoside at position 2′ by glycosyltransferase on position 2′ of chalcone.

FIG. 2 is a view showing alignments of amino acid sequences of glycosyltransferases derived from plants. Nucleotide sequences corresponding to the amino acid sequences indicated by arrows were used as primers. The DNA amplified by these were used for probes as GT conservative regions in Example 2. Boxed parts are homologous sequences among various GT. Abbreviations are as follows. MG 3GGT: morning glory 3GGT, GGT7: gentian 3GT, HGT8: verbena 5GT, Sb UFGT: Baikal skullcap GT.

BEST MODE FOR CARRYING OUT THE INVENTION

The gene of the present invention includes one encoding an amino acid sequence described in any of SEQ ID NOS: 2, 15, 17, 19, 21 or 56. However, it has been known that a protein having an amino acid sequence having addition, deletion or substitution of multiple amino acid residues keeps enzymatic activity equivalent to that of the original protein. Therefore, so long as the protein retains glycosyltransferase activity on position 2′ of chalcone, the protein having the amino acid sequence with addition, deletion and/or substitution of one or multiple amino acid residues in the amino acid sequence described in SEQ ID NOS: 2, 15, 17, 19, 21 or 56 and the gene encoding the protein belong to the invention. The multiple amino acid residues refer to 2 to 30, preferably 2 to 9 amino acid residues.

The present invention also relates to a gene which hybridizes with DNA having a nucleotide sequence complementary to a nucleotide sequence described in any of SEQ ID NOS: 1, 14, 16, 18, 20 or 55 under a stringent condition and encodes a protein having glycosyltransferase activity on position 2′ of chalcone. That is, the gene which hybridizes with DNA having the nucleotide sequence complementary to the nucleotide sequence described in any of SEQ ID NOS: 1, 14, 16, 18, 20 or 55 under a stringent condition and encodes the protein having glycosyltransferase activity at position 2′ of chalcone also belongs to the technical scope of the invention. Conditions of hybridization are different depending on lengths of DNA and nucleotide compositions used for a probe, and thus are not limited to concrete conditions shown by numerical values below. As referred to herein, the “stringent condition” is preferably 5×SSC and 37° C., more preferably 5×SSC and 50° C., and still more preferably 2×SSC and 65° C. Herein, the condition of 5×SSC and 37° C. may be applied as the condition where a homolog such as the glycosyltransferase on position 2′ of chalcone of the invention is hybridized using a conservative region of the glycosyltransferase gene of anthocyanidins as a probe as shown in Example 2. The condition of 5×SSC and 50° C. may be applied preferably as the condition where the gene (ortholog) of the glycosyltransferase on position 2′ of chalcone from other source is hybridized using the gene of the glycosyltransferase on position 2′ of chalcone derived from the carnation of the invention as the probe.

The gene selected by the aforementioned hybridization includes naturally occurring substances, e.g., those derived from plants, e.g., those derived from the cyclamen, but is not limited to those derived from the plants. That is, the gene of the glycosyltransferase on position 2′ of chalcone of the invention is not limited to the gene of the glycosyltransferase on position 2′ of chalcone derived from the carnation, and may be the gene of the glycosyltransferase on position 2′ of chalcone derived from the plants such as cyclamen and Paeonia lactiflora containing the glycoside having the sugar at position 2′ of chalcones, which is a ortholog of the gene. Any of the related genes may be used for breeding yellow flowers. The gene selected by the hybridization may be cDNA or genomic DNA.

The gene having homology to the conservative region in the glycosyltransferase is obtained by screening a cDNA library made from the carnation petals as shown in Example. DNA encoding the glycosyltransferase having the amino acid sequence modified from the amino acid sequence in SEQ ID NO:2 may be synthesized using DNA having the nucleotide sequence described in SEQ ID NO:1 by site-directed mutagenesis and PCR method known publicly. DNA encoding the glycosyltransferase having the amino acid sequence modified from the amino acid sequence in SEQ ID NO:15 may be also synthesized using DNA having the nucleotide sequence described in SEQ ID NO:14 by site-directed mutagenesis and PCR method known publicly. DNA encoding the glycosyltransferase having the amino acid sequence modified from the amino acid sequence in SEQ ID NO:17 may be also synthesized using DNA having the nucleotide sequence described in SEQ ID NO:16 by site-directed mutagenesis and PCR method known publicly. DNA encoding the glycosyltransferase having the amino acid sequence modified from the amino acid sequence in SEQ ID NO:19 may be also synthesized using DNA having the nucleotide sequence described in SEQ ID NO:18 by site-directed mutagenesis and PCR method known publicly. DNA encoding the glycosyltransferase having the amino acid sequence modified from the amino acid sequence in SEQ ID NO:21 may be also synthesized using DNA having the nucleotide sequence described in SEQ ID NO:20 by site-directed mutagenesis and PCR method known publicly. DNA encoding the glycosyltransferase having the amino acid sequence modified from the amino acid sequence in SEQ ID NO:56 may be also synthesized using DNA having the nucleotide sequence described in SEQ ID NO:55 by site-directed mutagenesis and PCR method known publicly. For example, a DNA fragment corresponding to an amino acid sequence to be modified may be obtained by treating cDNA or genomic DNA with restriction enzymes, and using this as a template, the site-directed mutagenesis or the PCR may be performed using primers corresponding to the desired modified amino acid sequence to yield a DNA fragment corresponding to the modified desired amino acid sequence. Subsequently, this DNA fragment in which modification is introduced may be ligated to DNA fragments encoding the other parts of the target enzyme.

Alternatively, to obtain DNA encoding the enzyme composed of a shortened amino acid sequence, DNA encoding a longer amino acid sequence than the target amino acid sequence, e.g., a full length amino acid sequence may be cut with a desired restriction enzyme. When the resulting DNA fragment does not encode the whole target amino acid sequence, a DNA fragment corresponding to an amino acid sequence of lacked parts may be synthesized and ligated.

The resulting glycosyltransferase gene may be identified to encode the protein which exhibits the glycosyltransferase activity on position 2′ of chalcone by expressing the glycosyltransferase gene obtained in this way using a gene expression system in Escherichia coli or yeast, and measuring the glycosyltransferase activity on position 2′ of chalcone in an extracted solution of the Escherichia coli or yeast. The glycosyltransferase activity on position 2′ of chalcone may be measured by absorbing chalcones which is a substrate of the glycosyltransferase activity on position 2′ of chalcone onto a gel filtration resin, subsequently reacting the gel filtration resin with the extracted solution of Escherichia coli or yeast transformed with the glycosyltransferase gene and analyzing the produced chalcone glycoside having the sugar at position 2′ by high performance liquid chromatography.

Furthermore, a protein of the glycosyltransferase on position 2′ of chalcone, which is a product of the gene may be obtained by expressing the gene of glycosyltransferase on position 2′ of chalcone in appropriate host cells. Alternatively, using an antibody against the protein or peptide having all or a part of the amino acid sequence described in SEQ ID NO:2, the gene of glycosyltransferase on position 2′ of chalcone derived from the other organism may be obtained by expression cloning. For the amino acid sequences of SEQ ID NOS: 15, 17, 19, 21 and 56, the same may be performed.

The present invention also relates to a recombinant vector, particularly an expression vector containing the gene of glycosyltransferase on position 2′ of chalcone, and a host cell transformed with the vector. As the host cell, a prokaryotic organism or a eukaryotic organism may be used. The host cells known conventionally and publicly such as bacteria belonging to Escherichia, e.g., Escherichia coli and bacteria belonging to Bacillus, e.g., Bacillus subtilis may be used. As eukaryotic cells, eukaryotic microorganisms, preferably yeast and filamentous fungi may be used. The yeast may include Saccharomyces yeast such as Saccharomyces cerevisiae, and the filamentous fungi may include Aspergillus fungi such as Aspergillus oryzae and Aspergillus niger, and Penicillium fungi. Furthermore, animal cells and plant cells may be used as the host cells, and as the animal cells, cell systems of a mouse, hamster, monkey and human are used. Additionally, insect cells, e.g., silk worm cells and an adult silk worm itself are used as the host cells.

The expression vector of the invention contains expression controlling regions such as promoter and terminator, and a replication origin depending on a biological species of the host to which they should be introduced. As the promoter for the bacteria, particularly the promoter of the expression vector in Escherichia coli, the promoters known conventionally and publicly, e.g., a trc promoter, a tac promoter, and a lac promoter may be used. As the promoter for the yeast, a glyceraldehyde 3-phosphate dehydrogenase promoter and a PHO5 promoter may be used. As the promoter for the filamentous fungi, promoters of amylase and trp C may be used. However, the promoters are not limited thereto. As the promoter for the animal cells, viral promoters such as SV40 early promoter and SV40 late promoter are used. The expression vector may be made according to standard methods using restriction enzymes and ligase. The host cells may be transformed with the expression vector according to the method known conventionally and publicly.

In construction of the plant expression vector, when using Agrobacterium, a binary vector such as pBI121 may be used, and when using a particle gun, an Escherichia coli vector such as pUC19 may be used. Furthermore, a plant transformed with the gene of glycosyltransferase on position 2′ of chalcone may be obtained by selecting plant cells transformed with the plant expression vector using a marker gene such as antibiotic resistant gene, and redifferentiating using a condition of an appropriate plant hormone and the like. A plant with modified flower color may be obtained by cultivating the transformed plant to bloom.

The objective glycosyltransferase on position 2′ of chalcone may be isolated and purified from a culture or a plant by culturing or cultivating the host cells or the transformed plant transformed with the expression vector, and using filtration, centrifugation, disruption of cells, gel filtration chromatography and ion exchange chromatography according to the standard methods.

The present invention is not limited to only the genes of glycosyltransferase on position 2′ of chalcone in the carnation and cyclamen. Sources for the gene of glycosyltransferase on position 2′ of chalcone may be plants, animals or microorganisms. So long as a protein which the gene encodes has the glycosyltransferase activity at position 2′ of chalcone, the gene may be similarly utilized for the conversion of flower colors. The present invention also relates to the use of the gene of glycosyltransferase on position 2′ of chalcone. A plant with modified flower color by introducing and expressing the gene of glycosyltransferase on position 2′ of chalcone in the plant, or a progeny plant thereof or tissue of these plants is within the technical scope of the invention, and a form of the tissue may be a cut flower.

With the use of a current technical level, it is possible to introduce a gene into a plant and express the gene constitutively or specifically for tissue. It is also possible to inhibit the expression of the target gene by an antisense method and a co-suppression method. Examples of plants capable of being transformed may include, but are not limited to, rose, chrysanthemum, carnation, snapdragon, cyclamen, orchid, Eustoma russelloanum, freesia, gerbera, gladiolus, gypsophila, kalanchoe, lily, pelargonium, geranium, petunia, torenia, tulip, rice plant, barley, wheat, rapeseed, potato, tomato, poplar, banana, eucalyptus, sweet potato, soybean, alfalfa, lupine, maize, cauliflower and periwinkle.

As another embodiment of the method for modifying the flower color, means for introducing the gene of glycosyltransferase on position 2′ of chalcone of the invention as in the above as well as inhibiting metabolism to convert THC to a substance other than chalcone glycoside having the sugar at position 2′ of chalcone may be employed. For example, a form where the gene of glycosyltransferase on position 2′ of chalcone of the invention is introduced as well as the expression of one or more genes selected from the gene group of CHI gene (EMBO J., 7:1257, 1988), flavanone 3 hydroxylase gene (F3H) of petunia (Britsh et al., European J. Biochemistry 217:745-754, 1993) and dihydroflavonol 4 reductase gene (DFR) (Beld et al., Plant Molecular Biology 13:491-502, 1989; Huits et al., Plant J., 6:295-310, 1994) is inhibited may be employed.

EXAMPLES

The present invention will be described in detail with reference to the following Examples. Molecular biological techniques were performed according to methods described in WO 96/25500 or Molecular Cloning (Sambrook et al., Cold Spring Harbor Laboratory Press, 1989) unless otherwise indicated.

Example 1 Construction of cDNA Library of Carnation Flower Petal

RNA was isolated from 5 g of fresh flower petals of yellow carnation by a method using guanidine thiocyanate/cesium chloride shown in detail in “Method in Molecular Biology” Vol. 2 (Humana Press Inc., 1984), and poly-A+RNA was purified using Oligotex dT30 (Nippon Roche KK). A cDNA library was constructed from this poly-A+RNA using cDNA synthesis Kit (Stratagene) and λZAPIIUni-XR vector Kit (Stratagene). The resulting library contained 1.6×10⁵ plaque forming units.

Example 2 Isolation of Full Length Gene of Glycosyltransferase on Position 2′ of Chalcone

DNA fragments composed of nucleotide sequences corresponding to conservative regions (regions indicated by paired arrows in FIG. 2) obtained by comparing the amino acid sequences of glycosyltransferases (GT) shown in FIG. 2 were amplified, and using them as probes, the cDNA library of the carnation described in Example 1 was screened. The compared amino acid sequences are 4 kinds of the amino acid sequences of UDP glucose: anthocyanidin 3-glycoside glycosyltransferase (3GGT) derived from the morning glory (amino acid sequence described in SEQ ID NO:13), UDP-glucose: anthocyanin 3-glycosyltransferase (3GT) derived from the gentian (Plant Cell Physiol., 37:711, 1996), UDP-glucose: anthocyanin 5-glycosyltransferase (5GT) derived from the verbena (J. Biol. Chem., 274:7405, 1999) and Scutellaria baicalensis glycosyltransferase (GT) (Planta 210:1006-1013, 2000). For each GT, an oligonucleotide which can amplify the conservative region indicated by arrows with opposed directions was made, and labeled by PCR with DIG labeling system (Roche Diagnostics) according to the condition recommended by the manufacturer. Then, 25 cycles of the reaction composed of 95° C. for 1 min, 55° C. for 1 min and 72° C. for 2 min were performed using the plasmid containing 1 ng of each cDNA as a template, and 100 ng or less of respective oligonucleotides as primers. Using a mixture where equivalent amounts of these PCR products were mixed as a probe of hybridization, the cDNA library derived from the carnation described in Example 1 was screened. The primers used for amplification of the conservative regions are as follows.

Oligonucleotide Sequences

Morning glory 3GGT 5′-GAA ATG GTC GGA TTG GCT GGG-3′: SEQ ID NO:3 5′-ACC TCC ACC CCA ACT TTC AGG-3′: SEQ ID NO:4 Gentian 3GT 5′-TGC CTC AAA TGG CTT CAA ACT-3′: SEQ ID NO:5 5′-CCA CCT TTC ACC CCA ACC CC-3′: SEQ ID NO:6 Verbena 5GT 5′-TGC CTC GAA TGG TTG AGC ACG-3′: SEQ ID NO:7 5′-CTC TCA CTC TCA CAC CCG-3′: SEQ ID NO:8 Scutellaria baicalensis GT 5′-CAC GAA TGC TTA GCA TGG CTC-3′: SEQ ID NO:9 5′-CTT ATT GCC CAC TGA AAC CCC-3′: SEQ ID NO:10

Screening of the library was performed using a non-radioactive system DNA detection kit (supplied from Roche Diagnostics). The hybridization was performed in 5×SSC containing 1% SDS and 30% formamide at 37° C. overnight. A filter was washed with 1×SSC and 1% SDS at 55° C. for 30 min. About 270 thousands of plaques were screened, and eventually about 30 clones containing the glycosyltransferase gene were obtained. Among these clones, one clone where the glycosyltransferase activity on position 2′ of chalcone had been identified by methods described in Examples 4 and 5 was obtained, the clone was designated as T170, and a total nucleotide sequence thereof was determined. The nucleotide sequence was determined by a primer walking method with synthetic oligonucleotide primers using a DNA Sequencer model 3100 (Applied Biosystems). The nucleotide sequence and the amino acid sequence encoded by the nucleotide sequence were shown in SEQ ID NOS:1 and 2, respectively.

Example 3 Amino Acid Sequence Analysis of Glycosyltransferase on Position 2′ of Chalcone, T170

pT170 contained the gene T170 of 1709 bp encoding a protein with molecular weight of 54.2 kDa composed of 490 amino acid residues. The amino acid sequence encoded by the T170 gene was compared with those of glycosyltransferases already reported, and consequently, exhibited 25% homology with GT derived from livingstone daisy (Plant J. 19, 509 (1999)) and 21% homology with 5GT derived from perilla and verbena. Software used was Clustal W included in MacVector ver. 6.0 (Oxford Molecule), and the analysis was performed under the condition of matrix blosum: 30, ketuple: 1, gap penalty: 3, topdiagonals: 5, and window size: 5. In BLAST search (the search was performed under the default condition. That is, under the condition of composition-based statistics: on, choose filter: low, complexity matrix: blosum 62, gap costs: existence 11 and extention 1), the homology with those of various GT was observed. For example, the 55% homology with betanidine 6GT derived from the livingstone daisy (Planta, 214:492, 2002), the 45% homology with tobacco GT induced by salicylic acid (Accession Number AB052557, Eur. J. Biochem., 268:4086, 2001), and the 44% homology with tobacco NTGT3 (Accession Number AB072918) were observed in amino acid sequences.

It is known that the enzymes having the same function and activity resemble in amino acid sequences and form a family. In also GT, as shown FIG. 2, 3GGT derived from the morning glory, 3GT derived from the gentian, 5GT derived from the verbena and GT derived from the Scutellaria baicalensis form the family. The amino acid sequence of the glycosyltransferase on position 2′ of chalcone of the invention exhibits only the low homology with the amino acid sequences of these 4 kinds of GT, and does not belong to this family. The glycosyltransferase of the invention exhibited the relatively high homology with the betanidine 6GT derived from the livingstone daisy, the tobacco GT induced by salicylic acid and the tobacco NTGT3 described above, but no glycosyltransfer activity on the chalcone has been identified in these GT.

Example 4 Expression of T170 Gene in Escherichia coli

Expression of the T170 gene in Escherichia coli was performed using The QIA expressionist (Qiagen). First, to introduce an Nco I recognition sequence at 5′ side of an initiation codon of the glycosyltransferase gene on the T170, a PCR reaction was performed using two primers, T170-NcoI and M13M4 shown below.

T170-NcoI: 5′-AGT TCA ACC ATG GGC AAA GCA C-3′ (SEQ ID NO:11) M13M4: 5′-GTT TTC CCA GTC ACG AC-3′ (SEQ ID NO:12)

A PCR reaction mixture (25 μL) is composed of 100 ng of T170, 1× Ex-Taq buffer (Takara), 0.2 mM dNTPs, 0.2 pmol/μL of respective primers and 1.25 U of Ex-Taq polymerase. After reacting at 94° C. for 5 min, 25 cycles of the reaction of 94° C. for 1 min, 55° C. for 1 min and 72° C. for 2 min were performed, and finally the reaction solution was treated at 72° C. for 7 min. The resulting PCR product was subcloned into a pCR2.1 TOPO vector (Invitrogen) according to the method recommended by the manufacturer. A plasmid obtained in this way was designated as the plasmid pTOPO-T170. It was confirmed by sequencing that there was no error in the PCR reaction. pQE60 (Qiagen) was digested with Nco I and Bgl II, and subsequently an oligonucleotide cassette where complementary primers, pQE61-f and pQE61-r had been annealed was inserted in the same site to prepare a vector pQE-61 wherein MCS had been newly introduced.

(SEQ ID NO:36) (pQE61-f) 5′-CATGGGAGGTACCACTAGTGATATCA-3′ (SEQ ID NO:37) (pQE61-r) 5′-GATCTGATATCACTAGTGGTA CCT CC-3′

An about 1.8 kb fragment obtained by treating the plasmid pTOPO-T170 with restriction enzymes, Nco I, Kpn I and Pst I was ligated to sites of the vector pQE-61 cut with Nco I and KpnI to yield a plasmid pSB1443. Competent high JM109 (Toyobo) was transformed with pSB1443.

Example 5 Measurement of Glycosyltransferase Activity of T170 cDNA Recombinant Protein

The transformed Escherichia coli (E. coli) strain obtained in Example 4 was cultured in 3 ml of LB medium containing 50 μg/mL of ampicillin at 37° C. overnight with shaking. Then, 200 μL of the culture was added in 10 mL of an M9 medium containing 50 μg/mL of ampicillin and 0.5% casamino acids, and cultured until A600=0.6 to 1.0 was accomplished. Subsequently, IPTG (isopropyl-β-D-thiogalactopyranoside) was added at a final concentration of 0.02 mM, further the cultivation was continued at 27° C. overnight with shaking, and bacteria were collected by cold centrifugation (3,000 rpm, 10 min, 4° C.). Microbial cells were suspended in 10 mL of buffer (30 mM Tris-HCl, pH 7.5, 30 mM NaCl), E. coli was ultrasonically disrupted, then the centrifugation (15,000 rpm, 10 min, 4° C.) was performed, and the resulting supernatant was used as a crude enzyme solution for the following activity measurement.

THC (500 μg/mL in ethanol) was loaded on gel filtration resin, 1 mL of Toyopearl HW-40F (Tosoh) equilibrated with distilled water with diluting with 3 mL distilled water, and then washed with water. To 100 μL of this resin, 200 μL of the crude enzyme solution and 10 μL of 5 mM of UDP-glucose were added, and reacted at 30° C. for 2 hours. After removing a centrifuged supernatant and washing with water, the reaction was stopped by adding 300 μL of 50% acetonitrile containing 0.1% TFA (trifluoroacetic acid). Flavonoid was separated from the resin by ultrasonic treatment. The solution was centrifuged at 15,000 rpm at 4° C. for 5 min. The resulting supernatant was filtrated with a filter (pore size 0.45 μm, 4 mm, Millex-LH, Millipore) to remove insoluble substances, and then analyzed by high performance liquid chromatography. Analytical conditions of the chalcone and a glycoside thereof are as follows.

YMC-ODS-A312 (6 mmφ×150 mm, K.K. YMC) was used for a column, and H₂O containing 2% acetic acid was used as A solution and methanol was used as B solution in a mobile phase. Elution was performed with linear concentration gradient of 15% to 40% of B solution for 15 min, then kept at 40% of B solution for 5 min, further performed with linear concentration gradient of 40 to 62% of B solution, and subsequently kept at 62% of B solution for 2 min. A flow rate was 1.0 mL/min. Detection was performed by absorbance at 360 nm and absorption spectrum at 250 to 400 nm using a PDA detector, SPD-M6A (Shimadzu Corporation). Using standard preparations of THC and the glycoside having the glucose at position 2′ of THC, it was confirmed that the THC and the glycoside having the glucose at position 2′ thereof was eluted at retention time of 27.3 min and 19.89 min, respectively.

The extracted solution of E. coli in which the glycosyltransferase gene derived from the T170 had been expressed was reacted, and consequently, a new substance eluted at 19.89 min was detected in addition to THC (retention time: 27.3 min). This is believed to be a product produced by the glycosyltransferase derived from the T170 because no new substance was detected in the reacted crude extracted solution similarly prepared from E. coli in which the pQE-61 vector alone has been expressed.

From the above results, it has been confirmed that the glycosyltransferase derived from the T170 has the activity to transfer the glucose to a hydroxyl group at position 2′ of the THC.

Example 6 Construction of Expression Vector of T170 for Plant

In order to demonstrate the function of the gene product of the glycosyltransferase on position 2′ of chalcone derived from the T170 in the plant, a binary vector (pSPB1342) was constructed. The vector allowed to express c DNA T170 encoding the protein having the activity to transfer the sugar to the position 2′ of THC whereas to inhibit the expression of CHI-A gene (EMBO J., 7:1257, 1988), one of CHI genes encoding the protein having chalcone isomerase activity derived from the petunia, sharing the substrate with the present enzyme. The vector pSPB1342 was prepared as follows.

Total RNA was extracted from leaves of the petunia (cultivar: baccarat red, Sakata Seed Co.) using RNeasy Plant Mini Kit (Qiagen), and cDNA was synthesized from the RNA using Super Script™ First-Strand Synthesis System for RT-PCR (Invitrogen). Petunia CHI gene fragments of 0.6 kb and 0.8 kb were obtained from this cDNA by PCR using primers, BamHI-CHI-F (SEQ Id NO:49) and Sal-CHI-R (SEQ Id NO:50), Sal-CHI-F (SEQ Id NO:51) and EcoRI-CHI-R (SEQ Id NO:52), respectively. The resulting fragments were digested with BamH I and EcoR I, and Sal I and EcoR I, respectively to make the petunia CHI gene fragments. Meanwhile, pE2113 (Mitsuhara et al., Plant Cell Physiol., 37:45-59, 1996) has a cauliflower mosaic virus 35S (El235S) promoter where enhancer sequences are repeated and a nopaline synthase (nos) terminator. pUE6 was obtained by digesting pE2113 with SnaBI and inserting a BamH I linker. The pUE6 was digested with SacI to make a blunt end, and a Sal I linker (e.g., Takara) was inserted. This plasmid was digested with Hind III and EcoR I to yield DNA fragments. Among these fragments, the fragment having an El235S promoter was inserted at the Hind III-EcoR I site of pBINPLUS (vanEngelen et al., Plant Mol. Biol., 15:373, 1995), a binary vector for plant transformation. pSPB1601 was obtained by ligating an DNA fragment obtained by digesting this plasmid pSPB176 with BamH I and Sal I to the aforementioned two CHI gene fragments of the petunia. This pSPB1601 was digested with Asc I, and then dephosphorylated.

Subsequently, a cDNA fragment of about 1.5 kb was obtained by digesting the T170 gene inserted at a multiple cloning site, EcoR I-Xho I site of pBluescript II (sk⁻) (Stratagene) with BamH I (5′ end side of cDNA) and Kpn I (3′ end side of cDNA). A T170 gene expression cassette (pSPB1500) composed of an MAC1 promoter (Plant Mol. Biol., 15:373, 1990), the T170 gene and a mannopine synthetic enzyme (mas) terminator was constructed on the pUCAA, the plasmid that Pac I site of pUCAP (van Engelen et al., Transgenic research 4:288-290, 1995) had been substituted with Asc I linker. The cassete was placed between a portion of pUCAA cut with Hind III as 5′ end and a portion of the pUCAA cut with EcoR I as 3′ end.

BamHI-CHI-F: (SEQ ID NO:49) 5′-tttggattctttatattcatgtaatcttagaac-3′ Sal-CHI-R: (SEQ ID NO:50) 5′-tttgtcgacgtttacaacatcaggcccatttg-3′ Sal-CHI-F: (SEQ ID NO:51) 5′-tttgtctactttatattcatgtaatcttagaac-3′ EcoRI-CHI-R: (SEQ ID NO:52) 5′-tttgaattctattgattccagcactgcttcag-3′

The plasmid, pSPB1342 was prepared by recovering the whole T170 expression cassette constructed as the above by cut with Asc I and inserting at the site of the aforementioned pSPB1601 cut with Asc I in the same direction of the petunia CHI expression-inhibiting cassette, i.e., such that both left border sites (LB) of the binary vectors were upstream.

Subsequently, Agrobacterium with pSBP1342 was prepared, a leaf disk of the petunia (cultivar: PL) was transformed by an Agrobacterium method using the leaf disk. The transformation was performed according to the method known publicly (Plant J., 5:81, 1994).

Example 7 Expression of T170 and Change of Flavonoid Composition in Plant

The vector pSPB1342 prepared in Example 6 was introduced into Agrobacterium tumefaciens Agl0 (Lazo et al., Bio/Technology 9:963-967, 1991), and the petunia (cultivar: PL) leaf disk was transformed therewith by the Agrobacterium method using the leaf disk. Introduction of the plasmid into Agrobacterium and the transformation were performed according to the method known publicly (Plant J., 5:81, 1994). The flower color of the cultivar PL is white or pale pink because a flavonoid 3′,5′-hydroxylase gene (Holton et al., Nature 366:276-279, 1993) and a flavonoid 3′-hydroxylase gene (Brugliera et al., Plant J., 19:441-451, 1999) are deleted. In the object of the experiment of the invention, the cultivar of the petunia is not limited to PL.

As in the above, 61 strains of independently transformed petunias were obtained. Total RNA was extracted from flower petals of the petunia using RNeasy Plant Mini Kit (Qiagen). A reverse transcription reaction of 1 μg of this total RNA was performed using Superscript First-Strand Synthesis System for RT-PCR (Invitrogen). Further, RT-PCR was performed using Ex Taq (Takara) by the method recommended by the manufacturer. The primers T170F and T170R were used for the amplification of T170 mRNA. The primers CHIF1 and CHIR1 were used for the amplification of petunia CHI mRNA. The sequences of the primers are as follows.

T170F: 5′-GAGCAAAGCACCGTTCGAGTT G-3′ (SEQ ID NO:22) T170R: 5′-CTCCGTACATGATTGCAGAGAGCA-3′ (SEQ ID NO:23) CHIF1: 5′-GCAAAAATGTCTCCTCCAGTGTCC-3′ (SEQ ID NO:24) CHIR1: 5′-ACTTCTCAATGGCACGACCCTC-3′ (SEQ ID NO:25)

As a result, the T170 mRNA was detected in the petunia flower petals of 38 strains, and the reduction of petunia CHI mRNA was observed in 32 strains of the petunia.

The flower petals (0.5 g) of the petunia where the T170 mRNA had been detected was immersed in 50% acetonitrile containing 0.1% trifluoroacetic acid to extract flavonoid, which was then analyzed by high performance liquid chromatography (HPLC). As the condition for HPLC, the same condition as that in Example 5 using ODS-A-312 (150×6.0 mm) was employed. Under this condition, the glycoside having glucose at position 2′ of chalcone and the glycoside having glucose at position 4′ of chalcone were eluted at retention time of 19.89 min and 21.69 min, respectively. Three strains in the petunias which had expressed the T170 had a peak corresponding to the glycoside having glucose at position 2′ of chalcone, and also had the same absorption spectrum. Furthermore, the extract of the petunia flower petals and the glycoside having glucose at position 2′ of chalcone were analyzed by co-chromatography, and consequently, the peaks of the both were completely identical. From the above results, it could be shown that the glycoside having glucose at position 2′ of chalcone had been synthesized by the expression of the T170, i.e., T170 encoded the functional glycosyltransferase on position 2′ of chalcone. In the transformed petunia, although the amount of petunia CHI mRNA was decreased, the transcription thereof at a low level was observed.

Example 8 Construction of T170 Expression Vector for Plant

The glycoside having glucose at position 2′ of chalcone was insufficiently accumulated only by the expression of the T170 and the inhibition of the petunia CHI gene. Therefore, the expression of flavanone 3 hydroxylase gene (F3H) (Britsh et al., European J. Biochemistry 217:745-754, 1993) or dihydroflavonol 4 reductase gene (DFR) (Beld et al., Plant Molecular Biology 13:491-502, 1989; Huits et al., Plant J., 6:295-310, 1994) of petunia was inhibited.

(8-1) Construction of Petunia F3H cDNA Double Strand Construct

A PhF3H-1 fragment was obtained by performing PCR using pSPB265 where a petunia F3H cDNA gene had been cloned in pBluescript II (sk⁻) as the template and using a set of an M13RV primer (SEQ ID NO:48) and a PhF3H-1-ClaI primer (SEQ ID NO:40). This PhF3H-1 fragment was cloned using Zero Blunt TOPO PCR Cloning Kit (Invitrogen), and then cut out with Sac I and Cla I to prepare a PhF3H-1′ fragment of about 0.7 kb. Meanwhile, pSPB265 was digested with BamH I and Cla I and a fragment of about 0.9 kb was cut out to make PhF3H-2′. A blunt end was made at Asc I site of pUCAP (van Engelen et al., Transgenic research 4:288-290, 1995) and Pac I linker was inserted to construct a plasmid pUCPP. pUE6 was digested with EcoR I and Hind III. In the resulting fragments, a DNA fragment containing El235S promoter was inserted at a Hind III-EcoR I site of pUCPP. This plasmid was designated as pSPB540. pSPB1498 was constructed by ligating a DNA fragment of about 3.7 kb obtained by digesting pSPB540 with BamH I and Sac I to the PhF3H-1′ and PhF3H-2′ fragments. Consequently, this pSPB1498 employs a structure capable of transcripting dsF3H under the control of an El235S promoter and an NOS terminator.

Subsequently, a binary vector pSPB2201 where three genes, T170, dsCHI and dsF3H aligned in the same direction was constructed by introducing about 2.6 kb of gene cassette obtained by digesting pSPB1498 (dsPhF3H) with Pac I at the Pac I site of the binary vector pSPB1342 containing T170 and dsCHI. M13RV: 5′-caggaaacagctatgac-3′ (SEQ ID NO:48) PhF3H-ClaI: 5′-tggttcctggatcagtgtgtcttttc-3′ (SEQ ID NO:40)

(8-2) Construction of Petunia DFR cDNA Double Strand Construct

A plasmid pCGP1403 (WO 96/136716) containing the petunia DFR gene was digested with BamH I and Sca I, and Pvu II and Sac I to obtain 0.85 kb and 0.45 kb of fragments, respectively. A cassette composed of these both fragments which formed double strand RNA structures, an El235S promoter (Mitsuhara et al., Plant Cell Physiol., 37:49) and a mas terminator was inserted between Hind III-EcoR I of MCS of pBINPLUS (vanEngelen et al., Plant Mol. Biol., 15:373, 1995), a binary vector for the plant transformation to construct a plasmid pSPB532. This was digested with Pac I, and then dephosphorylated.

Subsequently, an about 2.5 kb fragment was obtained by digesting pSPB1601 containing the cassette composed of the El235S promoter, the petunia CHI gene with double strand RNA structure and the NOS terminator described in Example 6 with Hind III and EcoR I. This was inserted between Hind III-EcoR I of the vector pUCPP to construct pSFL5. This was cut with Pac I. The plasmid pSFL13 was obtained by inserting the 2.5 kb fragment obtained from pUCPP vector at the Pac I cut site of pSPB532 in the same direction as that of the petunia DFR expression-inhibiting cassette, i.e., such that LB sides of the vectors were upstream in both expression cassettes. Subsequently, this was digested with Asc I, and then dephosphorylated. On the plasmid vector, pUCAA described in Example 6, the T170 gene cassette composed of an MAC1 promoter (Comai et al., Plant Mol. Biol., 15:373, 1990), the T170 gene and the mannopine synthase gene terminator was cut with Asc I, and the fragment was cut out from the pUCAA vector to obtain about 3.5 kb of the fragment. This was inserted at the Asc I cut site of aforementioned pSFL13 so as to be in the same direction as those of petunia DFR and CHI expression-inhibiting cassettes to obtain a plasmid, pSFL14.

Example 9 Isolation of Chalcone Glycosyltransferase Gene, T128

There was a possibility that a chalcone glycosyltransferase gene other than T170 might be present in the carnation, and thus the search was continued. The nucleotide sequence of cDNA included in the plasmid which was designated as pT128 and the amino acid sequence thereof were shown in SEQ ID NOS: 14 and 15. The cDNA included in pT128 contained a gene T128 encoding a protein with molecular weight of 55.2 kDa composed of 489 amino acid residues. The amino acid sequence encoded by the T128 was compared with those of the glycosyltransferases already reported as described in Example 3. Consequently, it exhibited 54% identity with GT derived from the livingstone daisy, 24% identity with 5GT derived from the verbena and 27% identity with the T170 in amino acid sequences.

Example 10 Expression and Activity Measurement of T128 Gene in E. coli

The expression of the T128 gene in E. coli was performed using The QIA expressionist (Qiagen) which was the same as the method described in Example 4. First, to introduce an Nco I recognition sequence at 5′ side of an initiation codon of the glycosyltransferase gene on T128, the PCR reaction as with Example 4 was performed using the primer T128-NcoI shown below and M13 M4 shown in Example 4.

T128-NcoI: 5′-ACAATTTCAGCCATGGGCAC-3′ (SEQ ID NO:26)

The resulting PCR product was subcloned into pCR2.1 TOPO vector (Invitrogen) according to the method recommended by the manufacturer. The plasmid obtained in this way was designated as pTOPO-T128. It was confirmed by sequencing that there was no error in the PCR reaction. A plasmid pSPB1441 was obtained by ligating an about 1.8 kb fragment obtained by treating the pTOPO-T 128 with restriction enzymes Nco I and Kpn I to the same sites of the pQE-61 vector (Qiagen). Competent high JM109 (Toyobo) was transformed with pSPB1441.

This transformed E. coli strain was cultured and a crude enzyme solution was obtained by the methods described in Example 5. Using this, the glycosyltransfer activity was measured using the chalcone as the substrate. An extracted solution of E. coli which had expressed the glycosyltransferase gene derived from T128 was reacted, and consequently new substances eluted at 19.89 min and 21.69 min were detected in addition to THC (retention time: 27.3 min). It was confirmed that the former was the glycoside having glucose at position 2′ of THC and the latter was the glycoside having glucose at position 4′ of THC by comparing the retention time of each standard preparation. These are believed to be the products produced by the glycosyltransferase derived from T128 because these were not detected when a crude extract solution similarly prepared from E. coli in which the pQE-61 vector alone had been expressed was reacted. From the above results, it has been confirmed that the glycosyltransferase derived from T128 has the activity to glycosyltransfer glucose to the hydroxyl groups at positions 2′ and 4′ of THC.

Example 11 Construction of T128 Expression Vector for Plant

In order to demonstrate the function of the gene product of the glycosyltransferase on position 2′ of chalcone derived from T128 in the plant, a co-expression binary vector (pSPB2108) was constructed. The vector allowed to express T128 whereas the expression of CHI-A gene encoding the protein having chalcone isomerase activity derived from the petunia, sharing the substrate with the present enzyme was inhibited. The vector pSPB2108 was prepared as with Example 6 as follows.

First, the pSPB1601 was digested with Asc I, and then dephosphorylated.

Subsequently, a T128 cDNA fragment was obtained by digesting the T128 gene inserted at a multiple cloning site of pBluescript II (sk⁻) with BamH I (5′ end side of cDNA) and Kpn I (3′ end side of cDNA). Subsequently, on the plasmid vector pUCAA, the T128 gene expression cassette composed of the MAC1 promoter, the T128 gene and the mannopine synthase gene terminator was constructed using BamH I cut site and Kpn I site of the pUCAA vector at the 5′ end and the 3′ end, respectively. This whole T128 expression cassette was cut out from the pUCAA vector by cutting with Asc I.

The plasmid pSPB2108 was obtained by inserting the expression cassette cut out from the pUCAA with Asc I at Asc I cut site of the aforementioned pSPB1601 in the same direction as that of the petunia CHI expression-inhibiting cassette, i.e., such that the LB side of the vectors in both cassettes were upstream.

Example 12 Isolation of Chalcone Glycosyltransferase Gene, CGT93

Using the T170 as a probe, 24,000 plaques of the carnation flower petal library were screened. A plasmid, pCGT93 was obtained by screening. The cDNA included in the pCGT93 contained a gene, CGT93 of 1443 bp encoding a protein with molecular weight of 52.8 kDa composed of 481 amino acid residues. The amino acid sequence encoded by the CGT93 was compared with those of the glycosyltransferases already reported as described in Example 3. Consequently, it exhibited 26% identity with GT derived from the livingstone daisy, 23% identity with 5GT derived from the verbena, and 63% identity with the T170 and 25% identity with the T128 in amino acid sequences. The nucleotide sequence comprising the gene included the pCGT93 and the amino acid sequence encoded by the nucleotide sequence were shown in SEQ ID NOS: 16 and 17.

Example 13 Expression and Activity Measurement of CGT93 Gene in E. coli

The expression of the CGT93 gene in E. coli was performed using The QIA expressionist (Qiagen) which was the same as the method described in Example 4. First, to introduce the Nco I recognition sequence at 5′ side of the initiation codon of the glycosyltransferase gene on the CGT93, the PCR reaction as with Example 4 was performed using the primers A93-75BspHI and A93-75-BglII shown below.

A93-75BspHI: 5′-ACAGGATCATGACTTCAGGG-3′ (SEQ ID NO:27) A93-75-BglII: 5′-GGAAGATCTAATATACGTGAGTAC-3′ (SEQ ID NO:28)

The resulting PCR product was subcloned into a pCR-Blunt II-TOPO vector (Invitrogen) according to the method recommended by the manufacturer. The obtained plasmid was designated as the plasmid pSPB1469. It was confirmed by sequencing that there was no error in the PCR reaction. This pSPB1469 was treated with restriction enzymes, BspH I and Bgl II, and the resulting about 1.8 kb fragment was ligated to the cut sites with Nco I and Bgl II of the pQE-61 vector to construct a plasmid, pSPB1470. Competent high JM109 was transformed with this pSPB1470.

This transformed E. coli strain was cultured and a crude enzyme solution was obtained by the methods described in Example 5. Using this, the glycosyltransfer activity was measured by the methods described in Example 5 using the chalcone as the substrate.

The extracted solution of E. coli in which the glycosyltransferase gene derived from CGT93 had been expressed was reacted, and consequently, a new substance eluted at 19.89 min was detected in addition to THC (retention time: 27.3 min). This is believed to be a product produced by the glycosyltransferase derived from the CGT93 because this was identical to the retention time of the glycoside having glucose at position 2′ of THC and no new substance was detected in the reacted crude extracted solution similarly prepared from E. coli in which the pQE-61 vector alone had been expressed.

From the above results, it has been confirmed that the glycosyltransferase derived from the CGT93 has the activity to transfer glucose to the hydroxyl group at position 2′ of THC.

Example 14 Construction of Expression Vector Containing CGT93 for Plants

In order to demonstrate the function of the gene product of the glycosyltransferase on position 2′ of chalcone derived from the CGT93 in the plant, a co-expression binary vector (pSPB1494) was constructed. The vector allowed to express the CGT93 whereas to inihibit the expression of CHI-A gene encoding the protein having the chalcone isomerase activity derived from the petunia, sharing the substrate with the present enzyme. The vector pSPB1494 was prepared as with Example 6 as follows.

First, the pSPB1601 was digested with Asc I, and then dephosphorylated.

Subsequently, the CGT93 gene inserted at the multiple cloning site of pBluescript II (sk⁻) was digested with Xho I (3′ end side of cDNA), then blunted using DNA Blunting Kit (Takara), and further digested with BamH I (5′ end side of cDNA) to obtain a CGT93 cDNA fragment. A plasmid pSPB184 composed of the MAC1 promoter and the mannopine synthase gene terminator was digested with Kpn I, then blunted using DNA Blunting Kit, and further digested with BamH I. The both of BamH I digested fragments above were inserted at this BamH I site on the plasmid vector pUCAA. A gene expression cassette pSPB1493 composed the MAC1 promoter, the CGT93 gene and the mannopine synthase gene terminator, and having a BamH I cut site of the vector at the 5′ end and a Kpn I site at the 3′ end was constructed.

The cassette pSPB1493 constructed in this way was cut out with Asc I as the whole CGT93 expression cassette from the vector pUCAA, and inserted at the aforementioned Asc I cut site of the pSPB1601 in the same direction as that of the petunia CHI expression-inhibiting cassette, i.e., such that the LB sides of the vectors were upstream in both expression cassettes to construct a plasmid which was designated as pSPB1494.

Example 15 Preparation of Subtraction Library

Poly-A+RNA was obtained from buds, flower petals and leaves of the yellow carnation by the method described in Example 1. A cDNA library where genes expressed in the flower petal were concentrated was prepared by the method recommended by the manufacturer using Clontech PCR-Select cDNA Subtraction Kit (Clontech). As a result of random sequencing, 16 clones having the homology to GC were obtained. These GT homolog clones obtained by subtraction did not have the full length. Therefore, 24,000 clones from the flower petal cDNA library were screened again using the GT homolog fragments as probes. The screening was performed according to the method described in Example 2.

Example 16 Isolation of Chalcone Glycosyltransferase Gene, S6B11

A nucleotide sequence of cDNA included in a plasmid designated as pS6B11 which was a clone obtained by the subtraction in Example 15 and an amino acid sequence thereof were shown in SEQ ID NOS 18 and 19 in Sequence Listing. The cDNA included in the pS6B11 contained a gene, S6B11 of 1449 bp encoding a protein with molecular weight of 54.4 kDa composed of 483 amino acid residues. The sequence was compared with those of the glycosyltransferases already reported as described in Example 3. Consequently, it exhibited 60% identity with GT derived from the livingstone daisy, 26% identity with 5GT derived from the verbena, as well as 27%, 54% and 27% identity with the T170, T128 and CGT93, in amino acid sequences.

Example 17 Construction of S6B11 Expression Vector for Plants

In order to demonstrate the function of the gene product of the chalcone glycosyltransferase derived from S6B11 in the plant, a co-expression binary vector (pSPB1335) was constructed. The vector allowed to express the S6B11 whereas to inhibit the expression of CHI-A gene encoding the protein having chalcone the isomerase activity derived from the petunia, sharing the substrate with the present enzyme. The vector pSPB1335 was prepared as with Example 6 as follows.

First, the pSPB1601 was digested with Asc I, and then dephosphorylated.

Subsequently, a S6B11 cDNA fragment was obtained by digesting the S6B11 gene inserted at the multiple cloning site of pBluescript II (sk⁻) with BamH I (5′ end side of cDNA) and Kpn I (3′ end side of cDNA). Subsequently, an S6B11 gene expression cassette composed of the MAC1 promoter, the S6B11 gene and the mannopine synthase gene terminator was constructed on the plasmid vector pUCAA at the cut site of Bam H I as 5′ end and the cut site of Kpn I as the 3′ end. This S6B11 expression cassette was entirely cut out with Asc I from the vector pUCAA.

The S6B11 expression cassette cut out as the above was inserted at the aforementioned Asc I cut site of the pSPB1601 in the same direction as that of the petunia CHI expression-inhibiting cassette, i.e., such that the LB sides of the vectors were upstream in both expression cassettes to construct a plasmid which was designated as pSPB1335.

Example 18 Expression of S6B11 and Change of Flavonoid Composition in Plant

As described in Example 7, the pSPB1335 was introduced into Agrobacterium tumefaciens Ag10, and the petunia PL strains were transformed therewith.

As a result, 27 strains of independently transformed petunias were obtained. The RT-PCR reaction as with Example 7 was performed using RNA of the petunia flower petals. The primers, S6B11-RT-F and S6B11-RT-R were used for the amplification of S6B11 mRNA, and the same CHIF1 and CHIR1 as those in Example 7 were used for the amplification of CHI mRNA. The sequences of the primers are as follows.

S6B11-RT-F: 5′-GTAATCCGCTCATCAATGTGGAG-3′ (SEQ ID NO:29) SGB11-RT-R: 5′-AGCAAATGGTTCGTCGTCAGAC-3′ (SEQ ID NO:30)

As a result, the S6B11 mRNA was detected in the flower petals in 24 petunia strains, and the reduction of CHI mRNA was observed in 11 petunia strains. Flavonoid was extracted from the flower petals of petunia in which the S6B11 mRNA had been detected, as is the case with Example 7, and analyzed by high performance liquid chromatography based on a methanol solvent using ODS-A-312. Among the petunias which had expressed the S6B11, 4 strains had a peak equivalent to the peak of the glycoside having glucose at position 2′ of chalcone and the same absorption spectrum. Further, an extract from the flower petals of petunia in which S6B11 had been expressed and the glycoside having glucose at position 2′ of chalcone were analyzed, and consequently both peaks were completely identical. The above could prove that the glycoside having glucose at position 2′ of chalcone was synthesized by the expression of S6B11, i.e., the S6B11 encoded the functional glycosyltransferase on position 2′ of chalcone in the plant. In the transformed petunia, although the amount of petunia CHI mRNA was decreased, the transcription at a low level was observed.

Example 19 Isolation of Chalcone Glycosyltransferase Gene, S12A2

The clone, pS12A2-a obtained by the subtraction in Example 15 deleted the 5′ region. An about 0.4 kb fragment (pS12A2-b) was TA-cloned by 5′-RACE using S12A2-RT, four primers, S12A2-S1, S12A2-A1, S12A2-S2 and S12A2-A2, and 5′-full RACE Core Set (Takara). The primers are shown below.

S12A2-NcoI: 5′-ACCAGACCATGGGTGCTG-3′ (SEQ ID NO:31) S12A2-S1: 5′-GAGATTGCAATGGGCATCC-3′ (SEQ ID NO:32) S12A2-S2: 5′-GTGGCCGACATGTTTTACCC-3′ (SEQ ID NO:33) S12A2-A1: 5′-GCATTCTCACAACCCTCAGG-3′ (SEQ ID NO:34) S12A2-A2: 5′-TCTGTTACCCGTGTCAACTGC-3′ (SEQ ID NO:35)

A fragment amplified by PCR with the S12A2-NcoI and S12A2-A2 using the pS12A2-b as the template was further TA-cloned again (pS12A2-c). A vector was constructed by introducing a fragment obtained by digesting pS12A2 with Nde I and Kpn I, wherein the fragment had been inserted, at the same site of pS12A2-c. Then a clone which contained the full length (pS12A2-d) was obtained. A nucleotide sequence of cDNA included in this plasmid and an amino acid sequence thereof were shown in SEQ ID NOS 20 and 21 in Sequence Listing. The cDNA included in pS12A2-d contained a gene S12A2 of 1458 bp encoding a protein with molecular weight of 55.0 kDa composed of 486 amino acid residues. The sequence was compared with those of the glycosyltransferases already reported as described in Example 3. Consequently, it exhibited 57% identity with GT derived from the livingstone daisy, 25% identity with 5GT derived from the verbena, as well as 27%, 52%, 27% and 67% identity with the T170, T128, CGT93 and S6B11, respectively in amino acid sequences.

Example 20 Expression and Activity Measurement of S12A2 Gene in E. Coli

Expression of the S12A2 gene in E. coli was performed using The QIA expressionist (Qiagen) according to the same method described in Example 4. The pS12A2-d in Example 19 was digested with Nco I and Kpn I, and ligated to the same site of the pQE-61 to construct pSPB1439. Competent high JM109 (Toyobo) was transformed with the pSPB1439.

This transformed E. coli strain was cultured by the methods described in Example 5 and a crude enzyme solution was obtained. Using this, the glycosyltransfer activity was measured using the chalcone as the substrate by the methods described in Example 5.

The extracted solution of E. coli in which the glycosyltransferase gene derived from the S12A2 had been expressed was reacted, and consequently, a new substance eluted at 19.89 min was detected in addition to THC (retention time: 27.3 min). This is believed to be a product produced by the glycosyltransferase derived from the S12A2 because no new substance was detected in the reacted crude extracted solution similarly prepared from E. coli in which the pQE-61 vector alone had been expressed. From the above results, it has been confirmed that the glycosyltransferase derived from the S12A2 has the activity to transfer glucose to the hydroxyl group at position 2′ of THC.

Example 21 Construction of Expression Vector of S12A2 for Plants

In order to demonstrate the function of the gene product of the chalcone glycosyltransferase derived from the S12A2 in the plant, a co-expression binary vector (pSPB1478) was constructed. The vector allowed to express the S12A2 whereas to in inhibit the expression of CHI-A gene encoding the protein having the chalcone isomerase activity derived from the petunia, sharing the substrate with the present enzyme. The vector pSPB1478 was prepared as with Example 6 as follows.

First, the pSPB1601 was digested with Asc I, and then dephosphorylated.

Subsequently, an S12A2 cDNA fragment was obtained by digesting the S12A2 gene inserted at the multiple cloning site of pBluescript II (sk⁻) with BamH I (5′ end side of cDNA) and Kpn I (3′ end side of cDNA). Subsequently, an S12A2 gene expression cassette composed of the MAC1 promoter, the S12A2 gene and the mannopine synthase gene terminator was constructed on the plasmid vector pUCAA at the cut site of BamH I as the 5′ end and the cut site of Kpn I as the 3′ ends. This S12A2 expression cassette was entirely cut out with Asc I from the vector pUCAA.

The S12A2 expression cassette cut out as the above was inserted at the aforementioned Asc I cut site of the pSPB1601 in the same direction as that of the petunia CHI expression-inhibiting cassette, i.e., such that the LB sides of the vectors were upstream in both expression cassettes to construct a plasmid which was designated as pSPB1478.

Example 22 Expression of T170 in Plants 2

As described in Example 7, the pSFL14 was introduced into Agrobacterium tumefaciens Ag10, and the petunia PL strains and baccarat red strains were transformed therewith. Likewise, the PL strains and baccarat red strains were also transformed with the pSPB2201.

Example 23 Construction of T170 Expression Vector for Plants

In order to express the T170 and accumulate the chalcone glycoside in plants, e.g., torenia and verbena other than petunia, a co-expression vector to inhibit flavanone 3 hydroxylase (F3H) derived from the torenia was constructed for the torenia. For the verbena, a co-expression vector where CHI derived from the verbena (Tapian, registered trademark) was inhibited and a co-expression vector where expression of both CHI and F3H (Hanatemari, registered trademark) genes was inhibited were constructed.

(23-1) Construction of Torenia F3H cDNA Double Strand Construct (dsF3H)

A cDNA library (Molecular Breeding 6:239, 2000) of torenia flower petals were screened using the petunia F3H gene as a probe by the method described in Example 2 to isolate a torenia F3H gene.

PCR was performed by using pSPB266 where a cDNA gene of torenia F3H was cloned at pBluescript II (sk⁻) as a template and using a set of an M13RV primer (SEQ ID NO:48) and a ThF3H-SalI1 primer (SEQ ID NO:41) to obtain a ThF3H-1 fragment. Likewise, the PCR was performed by using a set of a reverse primer and ThF3H-SalI2 primer (SEQ ID NO:42) to obtain a ThF3H-2 fragment. The ThF3H-1 fragment and the ThF3H-2 fragment were TA-cloned using TOPO TA cloning Kit (Invitrogen), and then the former was cut out with Sac I and Sal I to yield an about 0.75 kb fragment which was designated as ThF3H-1′. Meanwhile, the latter was cut out with BamH I and Sal I to obtain an about 0.9 kb fragment which was designated as ThF3H-2′. DNA containing the promoter, obtained by digesting the pUE6 with Hind III and EcoR I, was inserted at Hind III and EcoR I sites of the pUCAA. An about 3.8 kb DNA fragment obtained by digesting this with BamH I and Sac I was ligated to the ThF3H-1′ and ThF3H-2′ fragments to construct pSFL308. Consequently, this pSFL308 employs the structure having the dsF3H and the NOS terminator downstream of the El2355 promoter. An about 2.7 kb fragment obtained by digesting pSFL308 (dsThF3H) with Asc I was blunted, and then introduced at SamI site of pBINPLUS to construct pSPB2218. About 3.7 kb of the T170 gene cassette sandwiched between the Mac promoter and the mas terminator was cut out with Asc I from the pSPB1342, and introduced at Asc I site of the pSPB2218 to construct the binary vector in which two genes of T170 and dsF3H were loaded in the same direction (pSPB2223).

ThF3H-SalI1: 5′-ttctctgtcgacgcccattgcc-3′ (SEQ ID NO:41) ThF3H-SalI2: 5′-cgccgtgtcgactcgcttgaag-3′ (SEQ ID NO:42) (23-2) Construction of verbena (Hanatemari, Registered Trademark) dsF3H

A cDNA library (Plant Cell Physiol., 44:s122, 2003) of verbena flower petals were screened using the petunia F3H gene as a probe by the method described in Example 2 to isolate a verbena F3H gene.

A plasmid pSPB9 where a cDNA gene of verbena F3H was cloned into pBluescript II (sk⁻) was digested with BstX I, then blunted, and partially digested with BamH I to recover an about 1.1 kb of gene fragment, which was designated as HaF3H-1. The pSPB9 was digested with Sac I and Hae II to recover an about 0.7 kb gene fragment, which was designated as HaF3H-2. An about 3.8 kb DNA fragment obtained by digesting the pSPB540 with BamH I and Sac I was ligated to the HaF3H-1 and HaF3H-2 fragments to construct pSPB2501. This pSPB2501 employs the structure having the dsF3H and the NOS terminator downstream of the El235S promoter.

(23-3) Construction of verbena (Tapian, Registered Trademark) dsCHI

A cDNA library (Plant Cell Physiol., 44:s122, 2003) of verbena flower petals were screened using the petunia CHI gene as a probe by the method described in Example 2 to isolate a verbena CHI gene.

PCR was performed by using the pSPB2109 where a cDNA gene of verbena CHI was cloned into pBluescript II (sk⁻) as the template and using a set of an M13RV primer (SEQ ID NO:48) and a TpCHI-XbaI2 primer (SEQ ID NO:45) to obtain a TpCHI-1 fragment. Likewise, the PCR was performed by using a TpCHI-SalI primer (SEQ ID NO:43) and a TpCHI-XbaI1 primer (SEQ ID NO:44) to yield a TpCHI-2 fragment. The TpCHI-1 fragment and the TpCHI-2 fragment were cloned using Zero Blunt TOPO PCR Cloning Kit (Invitrogen), and then the former was cut out with BamH I and Xba I to yield an about 0.68 kb fragment, which was designated as TpCHI-1′. Meanwhile, the latter was cut out with Xba I and Sal I to obtain an about 0.5 kb fragment, which was designated as TpCHI-2′. A DNA fragment where a GUS gene region had been eliminated by cutting out with BamH I and Sal I from the pSPB176 was ligated to the TpCHI-1′ and TpCHI-2′ fragments to construct pSPB1486. Consequently, the pSPB1486 employs the structure having the dsCHI and the NOS terminator downstream of the El235S promoter. This pSPB1486 was digested with Pac I, and then a PacI-FseI adaptor where two oligo DNA of PacI-FseIF (SEQ ID NO:46) and PacI-FseIR (SEQ ID NO:47) had been annealed was introduced to prepare pSPB2508 where a Fse I site was newly introduced.

TpCHI-SalI: 5′-acgcagaaaaaagtcgactg-3′ (SEQ ID NO:43) TpCHI-XbaI1: 5′-gaggtgattgggtctagag-3′ (SEQ ID NO:44) TpCHI-XbaI2: 5′-atttctagagcaggtccgacaat-3′ (SEQ ID NO:45) PacI-FseIF: 5′-taactgcactgaggccggccagat-3′ (SEQ ID NO:46) PacI-FseIR: 5′-ctggccggcctcagtgcagttaat-3′ (SEQ ID NO:47) (23-4) Construction of verbena (Hanatemari, Registered Trademark) dsF3H+ verbena (Tapian, Registered Trademark) dsCHI

A 2.9 kb gene fragment obtained by digesting the pSPB2501 with Pac I was introduced at Pac I site of the pSPB2508 to construct pSPB2504.

(23-5) Construction of T170 Gene Expression Vector (T170+dsCHI) for verbena

A binary vector pSPB1287 where two gene cassettes of T170 and dsCHI was loaded was constructed by introducing the 3.7 kb T170 gene cassette produced by cutting out pSPB1500 in Example 6 with Asc I to the Asc I site of the pSPB1486.

(23-6) Construction of T170 Gene Expression Vector (T170+dsCHI+dsF3H) for verbena 2

An adaptor, EcoFse1R where oligo DNA of EcoFse1 (SEQ ID NO:57) and EcoFseR (SEQ ID NO:58) had been annealed was introduced to the EcoR I site of pUC19, and then an adaptor HinFse3R where oligo DNA of HinFseR (SEQ ID NO:59) and HinFseR3 (SEQ ID NO:60) had been annealed was introduced to the Hind III site to construct a vector (pSPB1838) where two Fse I sites were introduced to both end sides of the multiple cloning site of the pUC19. A plasmid pSPB2505 was constructed by blunting the 3.7 kb T170 gene cassette produced by cutting out pSPB1500 in Example 6 with Asc I, and then inserting at a blunted site after digesting the pSPB1838 with Hind III and EcoR I. This operation enables to cut out the T170 gene cassette using Fse I.

The 3.7 kb T 170 gene cassette obtained by digesting pSPB2505 with Fse I was introduced to the Fse I site of the pSPB2504 to construct pSPB2507. As a result, the pSPB2507 employs the structure where the three gene cassettes of dsCHI, T170 and dsF3H are aligned in the same direction.

Example 24 Expression of T170 in verbena

The plasmid pSPB1287 was introduced into Agrobacterium tumefaciens Ag10 (Biotechnology), and the verbena (cultivar: Hanatemari scarlet) was transformed according to Tamura's method (Tamura et al., Plant Cell Rep., 21:459-466, 2003).

According to the above, 7 strains of independently transformed verbena were obtained. The RT-PCR reaction was performed using RNA of the verbena flower petals according to the same manner described in Example 7. The same primers T170F and T170R as those in Example 7 were used for the amplification of T170 mRNA, and the expression amount of verbena CHI mRNA was confirmed by the amplification of an about 0.5 kb gene fragment using the TpCHI-SalI primer (SEQ ID NO:43) and the TpCHI-XbaI1 primer (SEQ ID NO:44). As a result, the T170 mRNA was detected in the verbena flower petals of 7 strains, and the reduction in the expression amount of the verbena CHI mRNA was observed in the verbena flower petals of 3 strains. It could be confirmed that the flower color of the flower petals of one strain (SaT170#7) in 7 strains in which the expression of T170 had been confirmed was paler than control red color and was slightly tinged with yellow.

Example 25 Expression of T128 and Change of Flavonoid Composition in Plants

As described in Example 7, the pSPB2108 prepared in Example 11 was introduced into Agrobacterium tumefaciens-Ag10, and the petunia PL strains were transformed therewith.

As a result, 37 strains of independently transformed petunias were obtained. The RT-PCR reaction as with Example 7 was performed using RNA of petunia flower petals. The primers, T128-F (SEQ ID NO:38) and T128-R (SEQ ID NO:39) were used for the amplification of T128 mRNA, and the same CHIF1 and CHIR2 as those in Example 7 were used for the amplification of CHI. The sequence of each primer is as follows.

T128-F: 5′-acgagttagaacccgagtatgctg-3′ (SEQ ID NO:38) T128-R: 5′-cagtgtgtcacgaatcctcctacg-3′ (SEQ ID NO:39)

As a result, the T128 mRNA was detected in the flower petals in 19 petunia strains, and the reduction of CHI mRNA was observed in 26 petunia strains. Flavonoid was extracted from the flower petals of petunia in which the T128 m RNA had been detected according to the same manner described in Example 7, and analyzed by HPLC in the same method as that in Example 5. Among petunias which had expressed T128, 2 strains had a peak equivalent to the peak of the glycoside having glucose at position 2′ of chalcone and the same absorption spectrum. Further, an extract from the flower petals of petunia in which the T128 had been expressed and the glycoside having glucose at position 2′ of chalcone were analyzed by co-chromatography, and consequently both peaks were completely identical. The above could prove that the glycoside having glucose at position 2′ of chalcone was synthesized by the expression of T128, i.e., the T128 encoded the functional glycosyltransferase on position 2′ of chalcone in the plant.

Example 26 Construction of T128 Expression Vector for Plant 2

(26-1) T128+Petunia dsCHI+dsF3H

An about 2.6 kb gene cassette obtained by digesting the pSPB1498 (dsPhF3H) with Pac I was introduced to the Pac I site of the binary vector, pSPB2108 having the T128 and dsCHI to construct a vector, pSPB1499 having three genes of the T128, dsCHI and dsF3H together.

(26-2) T128+Torenia dsF3H

The about 3.7 kb T128 gene cassette sandwiched between the Mac promoter and the mas terminator was cut out with Asc I from the pSPB2108, and introduced to the Asc I site of the pSPB2218 prepared in Example 23 to construct a binary vector where two genes of the T128 and dsF3H were loaded in the same direction (pSPB2224).

Example 27 Expression of T128 in Plant

As described in Example 7, the pSPB1499 was introduced into Agrobacterium tumefaciens Ag10, and the petunia PL strains were transformed therewith.

Example 28 Construction of CGT93 Expression Vector for Plant 2

(28-1) CGT93+Petunia dsCHI+dsF3H

An about 2.6 kb gene cassette obtained by digesting the pSPB1498 (dsPhF3H) with Pac I was introduced to the Pac I site of the binary vector pSPB1494 having the CGT93 and dsCHI to construct a binary vector pSPB2202 having three genes of the CGT93, dsCHI and dsF3H together.

(28-2) CGT93+Torenia dsF3H

The about 3.7 kb CGT93 gene cassette sandwiched between the Mac promoter and the mas terminator was cut out with Asc I from pSPB1494, and introduced to the Asc I site of the pSPB2218 prepared in Example 23 to construct a binary vector, where two genes of the CGT93 and dsF3H were loaded in the same direction (pSPB2225).

Example 29 Expression of CGT93 in Plants

As described in Example 7, the pSPB1494 was introduced into Agrobacterium tumefaciens Ag10, and the petunia PL strains were transformed therewith. The petunia PL strains and baccarat red strains were transformed with the pSPB2202.

Example 30 Construction of S6B11 Expression Vector for Plant

(30-1) S6B11+Petunia dsCHI+dsF3H

An about 2.6 kb gene cassette obtained by digesting pSPB1498 (dsPhF3H) with Pac I was introduced to the Pac I site of the binary vector pSPB1335 having the S6B11 and dsCHI to construct a binary vector pSPB2205 having three genes of the S6B11, dsCHI and dsF3H together.

(30-2) S6B11+Torenia dsF3H

The about 3.7 kb S6B11 gene cassette sandwiched between the Mac promoter and the mas terminator was cut out with Asc I from the pSPB1335, and introduced to the Asc I site of the pSPB2218 prepared in Example 23 to construct a binary vector where two genes of the S6B11 and dsF3H were loaded in the same direction (pSPB2226).

Example 31 Expression of S6B11 in Plant 2

As described in Example 7, the pSPB2205 was introduced into Agrobacterium tumefaciens Ag10, and the petunia PL strains were transformed therewith.

Example 32 Construction of S12A2 Expression Vector for Plant 2

(32-1) S12A2+Petunia dsCHI+dsF3H

An about 2.6 kb gene cassette obtained by digesting the pSPB1498 (dsPhF3H) with Pac I was introduced to the Pac I site of the binary vector pSPB1478 having the S12A2 and dsCHI to construct a binary vector pSPB2206 having three genes of the S12A2, dsCHI and dsF3H together.

(32-2) S12A2+Torenia dsF3H

The about 3.7 kb S12A2 gene cassette sandwiched between the Mac promoter and the mas terminator was cut out with Asc I from the pSPB2206, and introduced to the Asc I site of the pSPB2218 prepared in Example 23 to construct a binary vector where two genes of the S12A2 and dsF3H were laded in the same direction (pSPB2227).

Example 33 Expression of S12A2 in Plant

As described in Example 7, the pSPB1478 prepared in Example 21 was introduced into Agrobacterium tumefaciens Agl0, and the petunia PL strains were transformed therewith. The PL strains were also transformed with the pSPB2206.

Example 34 Construction of Cyclamen Flower Petal cDNA Library

A cDNA library was constructed from 5 g of fresh flower petals of the yellow cyclamen by the same method as that in Example 1. The resulting library was composed of 1.75×10⁶ plaque forming units (pfu).

Example 35 Isolation of Chalcone Glycosyltransferase Gene, YCy3-12

Using the T170 as a probe, 24,000 plaques of the cyclamen flower petal library were screened. A plasmid, pYCy3-12 was obtained. cDNA included in the pYCy3-12 contained a gene, YCy3-12 of 1446 bp encoding a protein with molecular weight of 54.3 kDa composed of 482 amino acid residues. The amino acid sequence encoded by YCy3-12 was compared with those of the glycosyltransferases already reported as described in Example 3. Consequently, it exhibited 28% identity with GT derived from the livingstone daisy, 24% identity with 5GT derived from the verbena, as well as 46%, 28%, 46%, 28% and 27% identity with the T170, T128, CGT93, S6B11 and S12A2 in amino acid sequences, respectively. The nucleotide sequence including the gene contained in pYCy3-12 and the amino acid sequence encoded by the nucleotide sequence are shown in SEQ ID NOS 55 and 56, respectively in Sequence Listing.

Example 36 Expression and Activity Measurement of YCy3-12 in E. Coli

Expression of YCy3-12 gene in E. coli was performed using The QIA expressionist (Qiagen) according to the same method described in Example 4. First, to introduce the Nco I recognition sequence at 5′ side of the initiation codon of the glycosyltransferase gene on the YCy3-12, PCR reaction was performed using the primers, YCy-3-12P1 (SEQ ID NO:53) and YCy-3-12P2 (SEQ ID NO:54) shown below as was the case with Example 4.

YCy-3-12P1: 5′-ccccatggagagggcagagctagcctttca-3′ (SEQ ID NO:53) YCy-3-12P2: 5′-aaagcttcacgaagagcgattgagtacttc-3′ (SEQ ID NO:54)

The resulting PCR product was subcloned into a pCR-Blunt II-TOPO vector (Invitrogen) according to the method recommended by the manufacturer. The plasmid obtained in this way was designated as the plasmid pTOPO-YCy3-12. It was confirmed by sequencing that there was no error in the PCR reaction. An about 1.8 kb fragment obtained by treating pTOPO-YCy3-12 with restriction enzymes, Nco I and Hind III was ligated to the Nco I and Hind III sites of the pQE-61 vector to construct a plasmid, pQE-YCy3-12. Competent high JM109 was transformed with the pQE-YCy3-12.

This transformed E. coli strain was cultured and a crude enzyme solution was obtained by the methods described in Example 5. Using this, the glycosyltransfer activity was measured using the chalcone as the substrate by the methods described in Example 5.

The extracted solution of E. coli in which the glycosyltransferase gene derived from the YCy3-12 had been expressed was reacted, and consequently, a new substance eluted at 19.89 min was detected in addition to THC (retention time: 27.3 min). This is believed to be a product produced by the glycosyltransferase derived from the YCy3-12 because no new substance was detected in the reacted crude extracted solution similarly prepared from E. coli in which the pQE-61 vector alone had been expressed. From the above results, it has been confirmed that the glycosyltransferase derived from the YCy3-12 has the activity to transfer glucose to the hydroxyl group at position 2′ of THC.

INDUSTRIAL APPLICABILITY

The present invention is applied to industries related to flowers and ornamental plants, horticulture, plant breeding, agriculture and biotechnology.

Free Text in the Sequence Listing:

-   SEQ ID NO:3, Ipomoea purpurea 3GGT PN3GGTF -   SEQ ID NO:4, Ipomoea purpurea 3GGT PN3GGTR -   SEQ ID NO:5, Gentiana scabra 3GT GT3GTF -   SEQ ID NO:6, Gentiana scabra 3GT GT3GTR -   SEQ ID NO:7, Verbena hybrida 5GT H5GTF -   SEQ ID NO:8, Verbena hybrida 5GT H5GTR -   SEQ ID NO:9, Scutellaria baicalensis GT SBGTF -   SEQ ID NO:10, Scutellaria baicalensis GT SBGTR -   SEQ ID NO:11, T170-NcoI PCR primer -   SEQ ID NO:12, M13M4 PCR primer -   SEQ ID NO:13, An amino acid sequence of a protein having an activity     to transfer glucose to sugar at position 3 of flavonoids -   SEQ ID NO:22, T170F PCR primer -   SEQ ID NO:23, T170R PCR primer -   SEQ ID NO:24, CHIF1 PCR primer -   SEQ ID NO:25, CHIR1 PCR primer -   SEQ ID NO:26, T128-NcoI PCR primer -   SEQ ID NO:27, A93-75 BspHI PCR primer -   SEQ ID NO:28, A93-75-BglII PCR primer -   SEQ ID NO:29, S6B11-RT-F PCR primer -   SEQ ID NO:30, S6B11-RT-R PCR primer -   SEQ ID NO:31, S12A2-NcoI PCR primer -   SEQ ID NO:32, S12A2-S1 PCR primer -   SEQ ID NO:33, S12A2-S2 PCR primer -   SEQ ID NO:34, S12A2-A1 PCR primer -   SEQ ID NO:35, S12A2-A2 PCR primer -   SEQ ID NO:36, pQE61-f primer -   SEQ ID NO:37, pQE61-r primer -   SEQ ID NO:38, T128-F PCR Primer -   SEQ ID NO:39, T128-R PCR Primer -   SEQ ID NO:40, PhF3H-ClaI PCR Primer -   SEQ ID NO:41, ThF3H-SalI1 PCR Primer -   SEQ ID NO:42, ThF3H-SalI2 PCR Primer -   SEQ ID NO:43, TpCHI-SalI PCR Primer -   SEQ ID NO:44, TpCHI-XbaI1 PCR Primer -   SEQ ID NO:45, TpCHI-XbaI2 PCR Primer -   SEQ ID NO:46, PacI-FseIF adapter inserted in a vector -   SEQ ID NO:47, PacI-FseIR adapter inserted in a vector -   SEQ ID NO:48, M13RV PCR Primer -   SEQ ID NO:49, BamHI-CHI-F PCR Primer -   SEQ ID NO:50, Sal-CHI-R PCR Primer -   SEQ ID NO:51, Sal-CHI-F PCR Primer -   SEQ ID NO:52, EcoRI-CHI-R PCR Primer -   SEQ ID NO:53, YCy3-12P1 PCR Primer -   SEQ ID NO:54, YCy3-12P2 PCR Primer -   SEQ ID NO:57, EcoFseI Primer -   SEQ ID NO:58, EcoFseR Primer -   SEQ ID NO:59, HinFseR Primer -   SEQ ID NO:60, HinFse3 Primer 

1. An isolated polynucleotide encoding a protein comprising the amino acid sequence described in SEQ ID NO: 2 or an amino acid sequence having 1-30 amino acid substitutions in the amino acid sequence of SEQ ID NO: 2 and having an activity to transfer sugar to position 2′ of chalcones.
 2. A vector comprising the isolated polynucleotide according to claim
 1. 3. A host cell transformed with the vector according to claim
 2. 4. A method for producing a protein, which comprises culturing or growing the host cell according to claim 3, and collecting said protein having an activity to transfer sugar to position 2′ of chalcones from said host cell.
 5. A protein obtained by the method according to claim
 4. 6. A plant into which the isolated polynucleotide according to claim 1 has been introduced, or a plant which is a progeny of said plant, or tissue of said plant.
 7. A cut flower collected from the plant according to claim
 6. 8. A plant in which flower color has been modified by introducing and expressing the isolated polynucleotide according to claim 1 in the plant, and a plant which is a progeny of said plant.
 9. The plant according to claim 8, wherein a modified flower color is yellow. 